1. Field of the Invention
The present invention relates to a semiconductor device and, more particularly, to a semiconductor device provided with a capacitor formed by holding a paraelectric film between electrodes and to a method of manufacturing the semiconductor device.
2. Description of the Related Art
In semiconductor devices, including a dynamic random access memory (DRAM), elements are required to be integrated at a high density. As a result, a capacitor composing a memory cell is also required to be downsized. Capacitors of a conventional DRAM are formed by, for example, holding a dielectric film, such as a silicon nitride (SiN) film or a tantalum oxide (TaO) film, between conductor films, such as titanium nitride (TiN) films.
The capacitance of a capacitor have to be maintained while downsizing the capacitor. However, simply thin-filming the dielectric film in an attempt to maintain the capacitance of the capacitor causes the leakage current thereof to increase. Even in a case where an LTO (La-doped Ti oxide) film, the leakage current of which is smaller than that of a titanium oxide (Ti oxide) film, is used for the dielectric film, the leakage current increases drastically if the dielectric film is thinned to approximately 10 nm. Thickening the dielectric film in an attempt to prevent the increase of the leakage current results in the problem that the capacitor capacitance decreases. Accordingly, there is a need for a capacitor capable of minimizing a leakage current with an amount of capacitance change smaller than ever before.
Japanese Patent Laid-Open No. 9-260516 describes a capacitor structure element having a laminated structure composed of a lower electrode, a buffer layer (titanium oxide layer), a ferroelectric film (Bi4Ti3O12 film), an overcoat layer (titanium oxide layer) and an upper electrode, indicating that the capacitor structure element is applicable to ferroelectric memory devices. The publication also describes that forming the overcoat layer improves a leakage current characteristic and forming the buffer layer improves the symmetry of a hysteresis loop. However, techniques concerning this capacitor structure element are directed to solving problems specific to the use of a ferroelectric film.